/Engine/Source/Runtime/SlateCore/Public/Fonts/FontMeasure.h
Finds the first whole character index after the specified position in pixels along the string horizontally
The index of the first whole character after the specified horizontal offset
int32 FindFirstWholeCharacterIndexAfterOffset ( const [FString](API\Runtime\Core\Containers\FString) & Text, const [FSlateFontInfo](API\Runtime\SlateCore\Fonts\FSlateFontInfo) & InFontInfo, const int32 HorizontalOffset, float FontScale ) const